The Tundra
Biome provides examples of adaptation to extreme conditions.
About a fifth of the land surface of the earth is tundra.

The tundra biome is found next to
the icy zones in the arctic. (If there were land at those latitudes
in the southern hemisphere, tundra might be found there, too,
but this is not the case on earth right now.) There is also Alpine
Tundra high on the slopes of mountains. The first part
of this page is about arctic tundra. The two kinds of tundra
have many characteristics in common, including a very short growing
season and an absence of trees.

During most of the year, temperatures
on the tundra are below freezing, and may sometimes drop to as
low as -70 degrees Fahrenheit. There are powerful winds that
can blow up to 100 miles an hour. As a result of the cold, the
water in the ground freezes: the ground can be frozen
to a depth of 2000 feet or more. In some places only a few inches
of the top part of the ground thaw out in the summer, in other
places several feet may be thawed. The part of the ground that
thaws is called the active layer. This layer is
very wet, because the water from the melted ice cannot drain
away. The frozen ground that never thaws out is in the grip of
permafrost, and is called the permafrost layer.

Although
the tundra may get less than five inches of precipitation a year,
the area is still very wet in summer. (One inch of precipitation
(rain) = about ten inches of snow.) The water that comes
from the melting ice has nowhere to go. During the summer, the
whole landscape is one of open, gently rolling ground, covered
with many small lakes and ponds. The ground between the ponds
is soggy. During this time, the days are close to 24 hours long,
so that there is light for the little plants that grow wherever
the ground is not under water. On a warm day the temperature
may rise to 50 degrees Fahrenheit.

The plants in the tundra zone
are only about four inches high. Many of them are perennials,
building up food reserves in their roots from year to year. The
plants consist of grasses, sedges, mosses, little flowering plants,
and tiny dwarf willow bushes. They grow in shapes that protect
them from the cold, drying winds -- in dense round cushions,
or mats that hug the ground. Some of them have reddish leaves
to get as much energy as possible from the sun. In the rocky
places, lichens grow on the rocks. (Lichens were very early land
plants, and are a partnership between an alga and a fungus. They
have no roots.) Tundra plants must grow rapidly, because the
growing season lasts for only six to ten weeks. Many of
the plants reproduce vegetatively, by growing new roots and shoots,
rather than by making seeds. Spring starts in June when the ice
begins to melt, and winter returns by September.

The earth in
the tundra biome is not really considered to be a true soil. Dead
plant material decomposes very slowly because it is so cold.
(Chemical changes occur more quickly with more heat.) Water expands
when it turns to ice, and the constant melting and freezing of
the top of the ground moves the ground around. This results in
the ground being full of hollow spaces which serve as tunnels
for the lemmings that live in this biome. It also makes it impossible
for plants like trees, who have strong permanent root systems,
to live there.

Animal Life

Lemmings

Lemmings are small rodents.
They eat plants, weigh between an ounce and four ounces and are
three to five inches long. They look rather like hamsters, and
may be brownish or dark gray in the summer, when they live in
tunnels in the ground. They have short tails and fur on their
foot pads to help them to keep warm. In winter lemming fur turns
white, and the little creatures make tunnels under the snow and
eat the plants that they find.

The lemmings use the
r reproductive strategy, breeding very rapidly, hoping that
some members of their group can survive despite predators and
difficult weather conditions. After a 20 day pregnancy the mothers
produce litters of 6 to 9 babies, and the mothers soon become
pregnant again. A lemmiing can have 3 litters a year. More than
half of the new lemmings are female, and when they are a month
old they can also become pregnant.

Arctic Foxes

Arctic
foxes are year round predators in the tundra biome. These small,
dainty little animals are about the size of a cat, weighing six
to ten pounds. They have the warmest fur of any mammal, and look
fluffy. Their short legs, small ears, and short noses are adaptations
to reduce their surface area in the cold climate. They are brownish
in the summer and white in the winter. They hunt lemmings, chasing
them down in the summer and listening for them under the snow
in the winter time. They are very tough little animals and will
travel great distances when food is scarce.

Arctic foxes are very well adapted
to the cold. They even have fur on the bottoms of their feet.
Their metabolic rate increases when the temperature drops to
-50 degrees Celsius: at -70 degrees Celsius they start
shivering.

Arctic foxes may have one or
two litters of pups a year, but one litter is usual in the difficult
circumstances of the arctic tundra. Litter size is related to
the food supply. They may have no pups, or only one or two, when
food is scarce, and as many as twenty five when food is abundant.
A normal sized litter would be six to twelve pups. However, most
of these puppies will die of starvation before they are six months
old. The puppies are weaned between two to four weeks of age,
and survival on their own is difficult.

Because of the flexibility of
their reproductive patterns, arctic foxes can respond quickly
to increases in the number of lemmings. When there are more lemmings
the foxes have more pups, and more pups survive. The increase
in predators reduces the number of lemmings. Then some of the
foxes starve. This is repeated in four year cycles, although
mild or severe winters also have an effect on the population
numbers.

Snowy Owls

Snowy Owls are
well adapted to tundra life, although they will leave the area
to search for food in particularly severe winters.

They are small predators, weighing
two to four pounds. They are about two feet tall and have a wing
span that often exceeds five feet. Unlike most owls, they hunt
in the daytime as well as at night. This is an adaptation to
the 24 hour daylight that the tundra enjoys in summer. They also
change color, being brown in the summer and white in the winter.

Snowy owls prey on lemmings
and eat about a dozen lemmings each a day. They nest on the ground
on the highest and driest part of the tundra: there are
no trees in the tundra biome.

The female lays 8 - 10 eggs
and incubates the eggs for 33 days. The young start developing
in the eggs as soon as the eggs are laid, so that the owlets
are different sizes. This is a kind of insurance against sudden
storms or food shortages that might kill some of the chicks.
The young are ready to leave the nest in 16 days and begin to
fly at around the age of 52 days. The parents are kept busy feeding
the owlets.

Musk Oxen

Small herds of musk oxen also
roam the tundra. Groups of 10 or 12 of these peaceful grazers
eat the small plants and lichens. They are very hardy, and covered
with thick, soft, very warm fur. They weigh from 500 to 1000
pounds, and are between 3 and 6 feet high at the shoulder. Although
the tundra does not support wolves, wolves do attack musk oxen
when they wander into the bordering lands. Musk oxen have horns
for protection. When they are attacked they form a circle with
all the adults facing out and the young calves in the center.

Musk oxen use only a sixth of
the food that cattle need, so they must be processing what they
eat very efficiently. They take three years to mature and then
bear calves in alternate years. The calves drink milk for nine
months, while also eating plants. Contrast this slow reproduction
rate with the frenzied reproduction of the lemmings. These animals
are using the K Reproduction Strategy.

Other Animals

Other animals
found on the tundra in summer include reindeer, caribou, arctic
hares, and snow shoe rabbits. Reindeer and caribou migrate across
the tundra, eating lichen and plants. Arctic voles and mice are
also seen. Migrating birds may nest in the tundra areas near
the ocean, where there is more choice of food. Ptarmigans are
birds that stay in the arctic year round and change their brown
feathers to white when winters come. Summer insects include mosquitoes
and black flies.

This Fragile Ecosystem

Notice that
this biome has short food chains
and only a few species of animals. This is representative of
a challenging biome with a fragile ecosystem. Although the systems
function smoothly, the balance could be destroyed if a single
type of animal were to be wiped out by disease, over-hunting,
or predation. The plant systems are also fragile, and the ground
bears the marks of human traffic for many years. There is an
interesting contrast between the incredible hardiness of the
animals and plants that live here and their vulnerability to
outside stressors for which they are not prepared.

The Alpine Tundra

Tundra environments
also exist in the mountains above the tree line. The high meadows
are sprinkled with mountain flowers in the summer. These areas
are close to the forest area below, so there are more species
of animals present than are found in the Arctic tundra. Animals
are not totally dependent on the tundra vegetation, and can get
food from lower elevations or migrate down the mountain as winter
comes on. Marmots make their homes here, and mountain goats and
sheep spend their summers in the rocky crags.